1. Field of the Invention
The present invention relates to an improved method for cladding a steel core rod with another metal in such fashion that formation of objectionable oxides is resisted.
2. Brief Description of the Prior Art
It has been known for various reasons to clad a metal rod with another metal so as to obtain certain beneficial properties of the core material along with the surface or other characteristics of the cladding material while effecting certain economic benefits through the relatively limited use of the generally more expensive cladding material. See generally, U. S. Pat. Nos. 3,714,701; 4,227,061; and 4,331,283. In known systems it has been suggested to employ one or two metal cladding strips composed of a material, such as copper, for example which are preheated and may be preformed to enable solid phase bonding about the circumference of a preheated core rod member which may be composed of steel.
For many uses, the clad product is reduced in diameter, as by a drawing operation, in order to provide a uniformly clad product of the desired dimensions.
One of the problems which has been encountered with respect to the continuous cladding process, with particular emphasis on medium and high carbon steels core materials is that the required slow cooling procedures employed to avoid hardening of the steel core have also resulted in the formation of objectionable levels of oxides on the surface of the clad material. It has been known to try to obtain a clean rod surface for further processing by subsequently chemical cleaning, as by pickling, for example, or mechanically removing the surface oxide layer. It has also been known to enclose the slow cooling zone entirely in an inert or reducing atmosphere. These adjuncts to the main process are quite cumbersome.
We have previously suggested passing the clad rod, after suitable reduction of temperature by air cooling, through a reducing atmospheric chamber containing, for example, cracked ammonia, in order to reduce the previously formed oxide layer to the original metallic form. A meaningful problem with this approach is that the reduced metallic layer is porous and mechanically unstable as a direct result of the gaseous reduction process. This layer will tend to disintegrate during subsequent drawing or deformation processing to form a surface flake or dust which is highly objectionable and can interfere with subsequent processing or use of the clad product.
While it has previously been known to quench steel products in boiling water to effect reasonably rapid cooling while avoiding undesired formation of a circular transition products, it has not been previously suggested to employ boiling water quenches in respect of clad steel products in order to accomplish our objectives. See generally, Tendler, "Controlled Cooling of Rods", Wire Journal, February, 1981, pp. 84-91; "Hardening of Rail Steels by Quenching in Boiling Water", Industrial Heating, March, 1981 pp. 8-10; and Economopoulos et al., "The EDC Process: Metallurgical Background and Industrial Applications", Wire Journal, March, 1981, pp. 90-95.
There remains, therefore, a very real and substantial need for a process of producing a clean, continuously clad steel product which may be further processed and employed without cumbersome special atmosphere containing cooling enclosures or subsequent chemical or mechanical cleaning operations to eliminate oxide involvement or loss of metal either to oxide formation or through formation of metal sponge which is subsequently removed or falls off.